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I was robbed by a sweet old lady on a motorised cart.

'I' is the subject.
'was robbed' is the verb phrase and 'was' is the operator.
'by a sweet old lady on a motorised cart' is a prepositional phrase.
'sweet old lady' is the agent; what other semantical role(s) does this
noun-phrase play in the sentence? I mean, is it an object or what. No, it is not, I know, but then, what is it?
'by a sweet old lady' is a prepositional phrase.
'a sweet old lady' is a noun phrase.
'on a motorised cart' is a prep. phrase.
'on a motorised cart' is an adverbial phrase.

Question: Do you agree?
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I agree; it all looks good to me, Inchoate. Sweet old lady (as well as being the semantic agent) is just the noun-phrase object of the preposition by. By a sweet old lady... is an adverbial of agency.
Comments  
Thanks,